Why it matters: This staggering number of deaths "is at such a distance from official claims that, in terms of civilian deaths, this may be the least transparent war in recent American history," per NYT. It also raises questions about civilian casualties in neighboring Syria, and how far this reporting problem reaches around the world.

What they did, per the NYT: The reporters went to roughly 150 airstrike sites in northern Iraq to interview witnesses and local officials, photograph bomb fragments, search local records and news sources, and map out the destruction through satellite imagery. They visited the American air base in Qatar where the coalition is based and interviewed coalition officials and advisers. They provided coalition analysts with coordinates and date ranges of 103 air strikes to examine and compare their responses.

What they found, per the NYT: The coalition claims 1 civilian is killed in every 157 airstrikes but their on-the-ground analysis shows 1 civilian is killed in every 5 airstrikes. They added the coalition is doing a poor job of investigating claims or even to keep proper records to make investigation possible.

"While some of the civilian deaths we documented were a result of proximity to a legitimate ISIS target, many others appear to be the result simply of flawed or outdated intelligence that conflated civilians with combatants," according to Khan and Gopal.